Many embodiments of plasma torches currently exist. Generally speaking, a plasma torch, such as the one mentioned in the document U.S. Pat. No. 3,301,995, includes two coaxial tubular electrodes, each of the electrodes being disposed in a support surrounding it. The plasma torch also comprises means to produce the initiating of an electric arc between the two electrodes and means to inject a plasma gas, such as air, between the two electrodes simultaneously with the electric arc. Means for cooling the electrodes are also provided in each electrode support and are normally defined by a sealed cylindrical chamber provided in each support, a cylindrical separation wall dividing the sealed chamber into two concentric annular spaces communicating with each other at one end of said wall and through which a cooling fluid circulates.
In addition, as mentioned for example in the documents U.S. Pat. No. 3,301,995 EP-A-0 032 100, so as to avoid any premature wear of the electrodes, means are provided to move the catching feet of the electric arc onto the internal surfaces of the tubular electrodes. Generally speaking, these means are defined by at least one electromagnetic coil surrounding one of the electrode supports. Thus, by modulating the axial magnetic field generated by the coil when it is excited, the catching feet of the electric arc move around the internal surfaces of the electrodes, thus avoiding the formation of local craters and the rapid destruction of the electrodes.
However, the fitting of such a magnetic coil around the electrode carrier support requires significantly increasing the spatial requirement of the plasma torch so that in certain applications the plasma torches equipped as above do not satisfy the volume and shape requirements.
So as to reduce the external spatial requirement imposed by the coils, one solution consists of disposing them in an internal volume provided in each electrode support, as mentioned in the document U.S. Pat. No. 3,832,519. Nevertheless, the spatial requirement gain is not significant as the support is bigger, and in addition, the coils are provided with complex internal cooling circuits.